Childhood obesity and related co-morbidities such as type 2 diabetes have emerged as major public health challenges. Results from national surveys show that overweight and obesity trends have continued to rise. While treatment efforts are very costly and often not efficacious, prevention seems to be a more viable option. Understanding how obesity is related to health behavior is key to developing appropriate prevention strategies. As such, research efforts have focused on modifiable behaviors such as physical activity. Most studies show that boys are more active than girls, yet no study has developed an intervention in order to reduce these gender differences. Understanding key mediators and moderators of these gender differences will provide the necessary information for such studies. The long-term objectives are to gain an ecologically-oriented, empirically-based understanding of the determinants of gender differences in physical activity in children that will help in the development of gender- tailored interventions to promote physical activity in both boys and girls. The specific aims are to 1) develop new and/or modify existing measurement tools to assess key mediators and moderators of child's physical activity behaviors, and 2) conduct a cross-sectional study to implement these new tools to assess the gender-specific correlates of children's physical activity. This proposal will include the development, validation, and application of novel or refined measures to assess psychosocial, environmental and cultural correlates of physical activity in children aged 7-9 yrs old with a focus on gender. The first two years of training will be devoted to course work, analytical training, intense mentorship, development of instruments, and pilot testing of new or modifying existing measurement tools. The third through fifth years of training will involve conducting a cross-sectional study to implement these new measurement tools in a recreation center-based study (the NIDDK-funded parent grant) and analysis of data. Outcome measures will include child BMI, waist circumference, and physical activity via accelerometry. Independent variables will include: child, parental, community, cultural and environmental level data (i.e., child gender stereotypes, perceived barriers, parent support/modeling, acculturation, and availability of community physical activity programs). The relevance of this study is to give public health professionals critical information about what determines gender difference in physical activity of children. This information will be utilized to tailor physical activity programs for children so that both boys and girls can become more active, thus giving both equal opportunity to improve health and prevent obesity and type 2 diabetes.